Echographic investigation of the placenta has proved to be very valuable in monitoring pathological pregnancies. Precise localization of the placental area has led to a considerable increase in the practice of amniocentesis; placentography has enabled the authors to carry out biopsies of the placenta successfully. Diagnosis of gravidic metrorrhagia is greatly facilitated by echotomography, as long as the examination is carried out under good conditions, after filling of the bladder. A negative result may avoid the need for prolonged hospitalization. Systematic measurement of placental thickness at about the 36th week of pregnancy can detect unsuspected placental oedema or placental hypotrophy responsible for reduced intrauterine growth.